The invention disclosed herein relates generally to push button actuator mechanisms, and more particularly to push button actuator mechanisms which utilize a buckling column or beam to provide high tactile feedback with small button travel.
It is well known to equip electrical switches and similar devices with push button actuators. Such actuators may be fabricated as part of the switches, or may be separately fabricated and combined with one or more switches. For various applications it is desirable to use push buttons with small button travel. In keyboards, small button travel may help to alleviate operator fatigue. Where a push button actuated switches are positioned in close proximity, such as on keyboards and various other electronic equipment, small button travel may help to minimize inadvertent actuation of switches adjacent the intended switch. Also, push button actuator designs characterized by small button travel are generally simpler, less expensive and easier to manufacture.
One disadvantage generally associated with push button actuators with small button travel is diminished tactile feedback. Lack of tactile feedback contributes to ambiguity regarding whether a button has been depressed and switch actuation achieved. A special application specifically requiring push button switch actuators with high tactile feedback is on equipment which must be operated in a severe environment in which it is necessary for the operator to wear gloves. In such a situation, the tactile feedback must be sufficient to be easily detected through a glove.
A variety of mechanisms for enhancing tactile feedback in push button actuators with small button travel have been devised. One known type of such mechanisms comprises a column to which a longitudinal force or load is applied by actuation of the push button. The column is adapted to buckle in a transverse direction upon application of a sufficient force. This results in a distinct discontinuity in the force/travel relationship of the button as it is depressed. Specifically, force of less than a predetermined magnitude determined by the longitudinal load bearing capability of the column, does not result in significant movement of the button. However, as the load bearing capability of the column is exceeded, the column buckles resulting in sharply decreased load bearing capability. This causes the button to suddenly snap to its depressed position. Even where travel of the button is limited, a definite tactile response is produced.
Push button switches employing this phenomena are disclosed in a number of U.S. patents. Representative examples are shown in U.S. Pat. Nos. 4,002,871 and 4,002,879, both issued to D. Sims, Jr. Jan. 11, 1977.
The force/travel characteristic of a push button actuator employing a buckling column is generally solely determined by the parameters of the column (i.e., the cross sectional shape and the material from which it is made) which are fixed at the time the column is fabricated. Therefore, for an actuator having a given column, it is generally not possible to adjust the force required for actuation.
It is, however, pointed out that buckling of a column depends, not only on the magnitude of the longitudinal load, but on the manner in which it is applied. Thus, any asymmetry, such as might be caused by asymmetrical pressure on the button and/or wobble of the button in its mounting structure, may affect the magnitude of applied force at which the column buckles. In many applications, it is desired or required that the force required for actuation of a push button both fall within a narrow range of magnitudes and that it be repeatable.
The applicant has devised a unique mechanization and method for both providing adjustments of the required actuation force and insuring a repeatable force/travel actuation characteristic.